1994 PCED OBDI-A | SECTION 18A: Diesel Diagnosis — 7.3L DI Engine |
D1 DIAGNOSTIC TROUBLE CODE (DTC) 126:
CHECK FOR POWER TO MAP SENSOR
DTC 126 indicates the manifold absolute pressure (MAP) sensor is active but the frequency is out of self-test range.
Possible causes:
- MAP circuit open between sensor vehicle harness connector and PCM.
- Intermittent, MAP circuit shorted to VREF, SIG RTN, or GND.
- Damaged MAP sensor.
- Damaged PCM.
- SIG RTN or VREF circuit open at MAP sensor.
- Key off.
- Disconnect the MAP sensor from the vehicle harness.
- Connect the MAP tester between the vehicle harness connector and the MAP sensor.
- Insert MAP tester banana plugs into DVOM.
Note: Green light on tester indicates VREF is OK (4.5-5.5 volts). Red light (or no light) indicates VREF is either too low or too high. Tester reads approximately 1.1 volts at atmosphere.
- Key on.
Is green light on?
D2 CHECK FOR POWER AT SENSOR VEHICLE HARNESS CONNECTOR
Note: Green light reaffirms that VREF is OK (4.5-5.5 volts). Red light (or no light) indicates VREF is either too low or too high.
- Key on.
- MAP tester connected.
- DVOM connected to MAP tester.
- Disconnect MAP sensor.
Is green light on?
| Yes | No |
|---|
| REPLACE MAP sensor. RERUN Scan Tool Diagnostic Test. | REMOVE MAP tester. RECONNECT MAP sensor. GO to Pinpoint Test Step B1. |
D3 CHECK MAP CIRCUIT CONTINUITY DTC 127
- DTC 127 indicates that the MAP signal is inactive.
- Key off.
- MAP sensor disconnected.
- Disconnect powertrain control module (PCM). Inspect for damaged or pushed-out pins, corrosion, loose wires, etc. Service as necessary.
- Install breakout box, leave PCM disconnected.
- Measure resistance between signal return Pin C circuit at the MAP sensor vehicle harness connector and Test Pin 34 at the breakout box.
Is resistance less than 5 ohms?
| Yes | No |
|---|
| GO to D4. | SERVICE open circuit. REMOVE breakout box. RECONNECT all components. RERUN Scan Tool Diagnostic Test. |
D4 CHECK MAP CIRCUIT FOR SHORTS TO VREF, SIG RTN AND GROUND
- Key off.
- MAP sensor disconnected.
- Disconnect powertrain control module (PCM). Inspect for damaged or pushed-out pins, corrosion, loose wires, etc. Service as necessary.
- Install breakout box, leave PCM disconnected.
- Measure resistance between Test Pin 34 and Test Pins 90, 91, 51, 76, 77 and 103 at the breakout box.
Is each resistance greater than 10,000 ohms?
| Yes | No |
|---|
| REPLACE MAP sensor. REMOVE breakout box. RECONNECT PCM. RERUN Scan Tool Diagnostic Test. | SERVICE short circuit. REMOVE breakout box. RECONNECT all components. RERUN Scan Tool Diagnostic Test. |
D5 DIAGNOSTIC TROUBLE CODE (DTC) 128:
CHECK VACUUM HOSES
Continuous Memory DTC 128 indicates the MAP sensor vacuum has not changed more than 2 in-Hg (7 kPa) during normal vehicle operation.
Possible causes:
- MAP sensor vacuum supply hose improper routing, blockage and/or leakage.
- MAP sensor leak.
- Key off.
- Check vacuum hoses for proper routing. Refer to VECI decal. Check MAP sensor vacuum supply hoses for disconnections, kinks or blockage.
Are vacuum hoses OK?
| Yes | No |
|---|
| GO to D6. | SERVICE vacuum hoses as necessary. RERUN Scan Tool Diagnostic Test. |
D6 CHECK MAP SENSOR OPERATION
- Key off.
- Disconnect vacuum supply hose from MAP sensor.
- Install vacuum pump to MAP sensor.
- Apply 18 in-Hg (61 kPa) vacuum to MAP sensor.
Does MAP sensor hold vacuum?
| Yes | No |
|---|
| EEC System OK. RELEASE vacuum. REMOVE vacuum pump. RECONNECT vacuum supply hose to MAP sensor. GO to D7. | REPLACE MAP sensor. RECONNECT vacuum supply hose to MAP sensor. RERUN Scan Tool Diagnostic Test. |
D7 CHECK FOR CONTINUOUS MEMORY DIAGNOSTIC TROUBLE CODE (DTC) 126:
EXERCISE MAP/BARO SENSOR
Continuous Memory DTC 126 indicates the manifold absolute pressure (MAP) sensor was out of self-test range. The code was set during normal driving conditions. Correct range of measurement is typically from 1.4 to 1.6 volts.
Possible causes:
- Damaged MAP sensor.
- Damaged PCM harness.
- Damaged MAP sensor vehicle harness connectors and/or terminals.
- Unusually high/low barometric pressure.
- Using Key On, Engine Off Continuous Monitor Diagnostic Test Mode (DTM), observe STAR tester beeper for indication of a concern while performing the following:
- Connect the pressure side of the vacuum pump to the MAP sensor.
- Slowly apply 84 kPa (25 in-Hg) pressure to the MAP sensor.
- Slowly bleed pressure using a vacuum gauge off the MAP sensor.
- Lightly tap on MAP sensor (simulate road shock).
- Wiggle MAP connector.
Is fault indicated?
| Yes | No |
|---|
| DISCONNECT and INSPECT connectors. If connector and terminals are good, REPLACE MAP sensor. RERUN Scan Tool Diagnostic Test. | GO to D8. |
D8 CHECK EEC VEHICLE HARNESS
- Remain in Key On, Engine Off Continuous Monitor DTM.
- Observe VOM or STAR LED for a fault indication while performing the following:
- Grasp the vehicle harness closest to the sensor connector. Wiggle, shake or bend a small section of the closed loop system vehicle harness while working toward the dash panel. Also wiggle, shake or bend the PCM harness from the dash panel to the PCM.
Is a concern indicated?
| Yes | No |
|---|
| ISOLATE concern and SERVICE as necessary. CLEAR Continuous Memory Code. RERUN Scan Tool Diagnostic Test. | GO to D9. |
D9 CHECK PCM AND VEHICLE HARNESS CONNECTORS
- Key off.
- Disconnect PCM 104 pin connector.
- Inspect connectors and connector terminals for obvious damage or faults.
Are connectors and terminals OK?
| Yes | No |
|---|
| Unable to duplicate and/or identify concern at this time. RERUN Scan Tool Diagnostic Test. | SERVICE as necessary. RERUN Scan Tool Diagnostic Test. |
D: Introduction